Specialized variety of plant that is used to provide oxygen for space stations.

The new Director of the Venus Equilateral station goes on a routine inspection of the "air plant" and what does he find?

"I found that instead of a bunch of machinery, running smoothly, purifying air, and sending it out to the various parts of the station, all there was was a veritable jungle of weeds... I had some workmen clear the weeds out."

It turned out that the "air plant" was - Martian sawgrass.

"What better purifying machine is there than a plot of grass?" shouted Channing. "... We breathe oxygen, exhale CO2. Plants inhale CO2 and exhale oxygen. An air plant means just that. It is a specialized type of Martian sawgrass that uses chlorophyll... We've spent years getting that plant so it will grow just right. It got so good that the CO2 detectors weren't even needed...